Place half the spinach, with any water clinging to leaves, in a large pot over medium-high heat. Cover and steam 3 minutes or until wilted. Remove with tongs to a bowl and cover with cold water. Drain when cool. Gently squeeze spinach to remove excess water. Repeat with remaining spinach.

Wipe out pot, add butter and melt over medium-low heat. Add onion and cook, stirring occasionally, 7 minutes or until very soft. Remove from heat; stir in spinach and 1/4 teaspoon each of the salt and pepper.

Heat milk and cream in a small saucepan or in microwave until hot. Put flour and remaining 3/4 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Whisking constantly, gradually add hot milk mixture in a thin stream, whisking until well blended.

Heat oven to 425°F. Grease a shallow 2-quart baking dish.

Shred potatoes in a food processor or on the large openings of a box grater. Place in a large bowl of cold water for 5 minutes. Using hands, lift from water and spread on a kitchen towel. Cover with another towel and roll up to dry

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